Solid oxide fuel cell device (“SOFC” below) is a fuel cell device for generating electricity by causing an electrical generating reaction to take place at a relatively high temperature using an oxide ion electrically conductive solid electrolyte as an electrolyte, with electrodes attached on both sides thereof, and with fuel gas supplied to one side thereof and an oxidant (air, oxygen, etc.) supplied to the other side thereof.
In such SOFC, steam or CO2 is produced by the reaction between oxygen ions passed through the oxide ion conducting solid electrolyte with the fuel, thereby generating electrical and thermal energy. The electrical energy is extracted from the SOFC, where it is used for various electrical purposes. At the same time, thermal energy is transferred to the fuel, SOFC, oxidant, etc., and used to raise the temperature thereof.
It was common in the conventional SOFC to operate in a state whereby electrical generation output was held fixed, but when the SOFC is installed in facilities where there is virtually no electrical demand at night, or where there are large changes in electrical demand between day and night, etc., there is a need to vary the electrical generation output value in accordance with the amount of electrical generation required.
Patent Document 1 proposes an SOFC in which the SOFC operating condition can be stabilized in a short time period by controlling the SOFC to prevent sudden changes in SOFC reaction temperature when the electrical generation value is changed in accordance with the amount of electrical generation required.
In other words, in the SOFC of Patent Document 1, sudden changes in SOFC reaction temperature can be prevented by controlling the amount of oxidant supply and/or the oxidant temperature so that the SOFC reaction temperature T0 prior to the change in generation output at SOFC reaction temperature T satisfies “T0−10≦T≦T0+10.”